1. Field of the Invention
This invention relates to an electrophotographic photosensitive member containing a dis-azo pigment.
2. Description of the Prior Arts
As photosensitive members having layers containing organic pigments on a conductive layer known in the art, there are:
(i) a photosensitive member having a layer containing a pigment dispersed in an insulating binder provided on a conductive layer, as disclosed in Japanese Patent Publication No. 1667/1977 (Electrophotographic plate);
(ii) a photosensitive member having a layer containing a pigment dispersed in a charge transport medium, comprising a charge transport material or a combination of said material with an insulating binder (binder itself may be a charge transport material), provided on a conductive layer, as disclosed in U.S. Pat. No. 3,894,868 (Electrophotographic plate) and U.S. Pat. No. 3,870,516 (Electrophotographic imaging method);
(iii) a photosensitive member, comprising a conductive layer, a charge generation layer containing an organic pigment and a charge transport layer, as disclosed in U.S. Pat. No. 3,837,851 (Electrophotographic plate);
(iv) a photosensitive member, comprising an organic pigment added in a charge-transfer complex, as disclosed in U.S. Pat. No. 3,775,105 (Photoconductive member); and
(v) others.
As the pigments to be used in such photosensitive members, there have been proposed a great number of pigments such as phthalocyanine type pigments, polycyclic quinone type pigments, azo type pigments and quinacridone type pigments, but use of such pigment has scarecely been successful in practical application.
This is because an organic photoconductive pigment was inferior in sensitivity or durability, as compared with inorganic photoconductive materials such as Se, CdS or ZnO.
On the other hand, an inorganic photosensitive member also involves problems. For example, in case of Se-type photosensitive member, crystallization will proceed due to such factors as temperature, humidity, finger mark, etc. In particular, when the atmosphere surrounding photosensitive member exceeds a temperature of about 40.degree. C., crystallization is more pronounced, whereby there may be caused such disadvantages as lowering in charge bearing properties or formation of white spots on images. While the life of Se-type photosensitive member is said to be up to 30,000 through 50,000 copies, but there are much photosensitive members which cannot enjoy such a life, because of various environmental conditions depending on the regions and sites at which copying machines are placed.
The life of CdS type photosensitive member coated with an insulating layer is also similar to Se-type photosensitive member, but it is very difficult to overcome the drawback of poor humidity resistance. Under the present situation, a supplementary means such as heater is required to be used in order to prevent the photosensitive member from absorption of humidity.
In case of ZnO photosensitive member, it is sensitized with a dyestuff, typically Rose Bengal, and therefore there is such a problem as charge deterioration caused by corona discharge or colour fastness. At the present time, the life of this type of photosensitive member is about 1000 sheets of copies.
The sensitivities of photosensitive members, as represented by exposure quantity for halving original potential (E1/2) are about 15 lux.multidot.sec for unsensitized Se-type photosensitive member, and 4 to 8 lux.multidot.sec for sensitized one. The sensitivity of CdS type photosensitive member is similar to that of sensitized Se, while ZnO type photosensitive member has about 7 to 12 lux.multidot.sec of sensitivity.
As a sensitivity of practical photosensitive member, E1/2 value is desired to be 20 lux.multidot.sec or lower in case of a PPC copying machine, more preferably 15 lux.multidot.sec or lower for a high copying speed PPC copying machine. But, depending on uses, it is also possible to use a photosensitive member having a sensitivity lower than that mentioned above.